EH001: Lmx1a is an activator of Rgs4 and Gbr10 and is responsible for the correct specification of rostral and medial mdDA neurons

The LIM homeodomain transcription factor Lmx1a is a very potential inducer of stem cells towards dopaminergic neurons. Despite several studies on the function of this gene, the exact in vivo role of Lmx1a in mesodiencephalic dopamine (mdDA) neuronal specification is still not understood. To analyze the genes functioning downstream of Lmx1a, we performed expression microarray analysis of LMX1A overexpressing MN9D dopaminergic cells. Several interesting regulated genes were identified, based on their regulation in other, previously generated expression arrays, and their expression pattern in the developing mdDA neuronal field. Post analysis through in vivo expression analysis in Lmx1a mouse mutant (drJ/drJ) embryos demonstrated a clear decrease in expression of the genes Grb10 and Rgs4, in and adjacent to the rostral and dorsal mdDA neuronal field and within the Lmx1a expression domain. Interestingly, the DA marker Vmat2 was significantly up-regulated as a consequence of increased LMX1A dose, and subsequent analysis on Lmx1a mutant E14.5 and adult tissue revealed a significant decrease in Vmat2 expression in mdDA neurons. Taken together, microarray analysis of an LMX1A overexpression cell system resulted in the identification of novel downstream targets of Lmx1A in mdDA neurons: Grb10, Rgs4 and Vmat2. RNA was isolated from MN9D cells. Each experimental sample consisted of a RNA pool derived from 3 separate 10-cm dishes containing Lmx1a overexpressing MN9D cells (transfected with pcDNA3.1(-)-Lmx1a). microarray analysis was performed in triplicate, each experimental sample was hybridized to the same reference pool of RNA derived from 9 10-cm dishes containing control MN9D cells (transfected with empty pcDNA3.1(-)). On each of three microarray samples, dye swap was performed to correct for dye effects.